Surgical tool

ABSTRACT

Presented herein are dual-function surgical tools for insertion of implantable stimulating assemblies, such as intra-cochlear stimulating assemblies. In addition to facilitating intra-operative positioning of a stimulating assembly within a recipient (e.g., operating to guide the stimulating assembly of an implantable medical device into position), the surgical tool also includes a plurality of electrodes configured to apply an electroporation electrical field to a recipient&#39;s nerve cells to enable introduction of treatment substance into the nerve cells.

BACKGROUND Field of the Invention

The present invention relates generally to tissue-stimulatingprostheses.

Related Art

There are several types of medical devices that operate by deliveringelectrical (current) stimulation to the nerves, muscle or other tissuefibers of a recipient. These medical devices, referred to herein astissue-stimulating prostheses, typically deliver current stimulation tocompensate for a deficiency in the recipient. For example,tissue-stimulating hearing prostheses, such as cochlear implants, areoften proposed when a recipient experiences sensorineural hearing lossdue to the absence or destruction of the cochlear hair cells, whichtransduce acoustic signals into nerve impulses. Auditory brainstemstimulators are another type of tissue-stimulating hearing prosthesesthat might be proposed when a recipient experiences sensorineuralhearing loss due to damage to the auditory nerve.

SUMMARY

In one aspect, a surgical tool is provided. The surgical tool comprises:an intra-cochlear portion configured to be inserted into the cochlea ofa recipient to guide a stimulating assembly of an implantable medicaldevice into position within the cochlea, wherein the intra-cochlearportion of the surgical tool comprises a plurality of electrodes.

In another aspect, an insertion tool for an intra-cochlear stimulatingassembly is provided. The insertion tool comprises: an insertion guidetube having an insertion lumen configured to receive the intra-cochlearstimulating assembly therein, wherein a distal portion of the insertionguide tube is configured to be positioned within a cochlea of arecipient; and one or more electrodes disposed on the distal portion ofthe insertion guide tube, wherein the one or more electrodes areconfigured to apply an electrical field to the cochlea.

In another aspect, a method is provided. The method comprises:positioning a surgical tool in the cochlea of a recipient; generating anelectrical field between at least two electrodes disposed on anintra-cochlea portion of the surgical tool; advancing, via the surgicaltool, an electrode into the cochlea; and withdrawing the surgical toolfrom the cochlea.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of a cochlear implant having a stimulatingassembly that may be advantageously implanted in a recipient using anembodiment of an insertion tool described herein;

FIG. 2 is a side view of an embodiment of an insertion tool inaccordance with embodiments presented herein;

FIG. 3A is a schematic diagram illustrating a nerve cell prior tointroduction of a treatment substance therein via electroporation inaccordance with embodiments presented herein;

FIG. 3B is a schematic diagram illustrating an enlarged view of aportion of the nerve cell of FIG. 3A;

FIG. 3C is a schematic diagram illustrating the nerve cell of FIG. 3Aduring introduction of a treatment substance therein via electroporationin accordance with embodiments presented herein;

FIG. 3D is a schematic diagram illustrating an enlarged view of aportion of the nerve cell of FIG. 3C;

FIG. 4A is a perspective view of an intra-cochlear portion of aninsertion tool in accordance with certain embodiments presented herein;

FIG. 4B is a perspective view of an intra-cochlear portion of aninsertion tool in accordance with alternative embodiments presentedherein;

FIG. 5 is a schematic diagram illustrating an electroporation controlmodule in accordance with embodiments presented herein;

FIGS. 6A and 6B are cross-sectional diagrams illustrating an insertiontool having a collapsible lumen for delivery of treatment substances ora recipient's cochlea in accordance with embodiments presented herein;

FIG. 6C is a cross-sectional diagram illustrating another insertion toolin accordance with embodiments presented herein;

FIG. 7A is a cross-sectional view of an embodiment of an insertion guidetube in accordance with embodiments presented herein;

FIG. 7B is a perspective view of the portion of the insertion guide tubeillustrated in FIG. 7A;

FIG. 7C is a cross-sectional view of a stimulating assembly forimplantation into a recipient's cochlea;

FIG. 7D is a cross-sectional view of the stimulating assembly of FIG. 7Cpositioned in the insertion guide tube illustrated in FIGS. 7A and 7B;

FIG. 7E is a cross-sectional view of the stimulating assembly of FIG. 7Cpositioned in the insertion guide tube illustrated in FIGS. 7A and 7Bwith arrows representing the twisting force of the stimulating assemblyand the reactive force applied to the stimulating assembly by theinsertion guide tube;

FIG. 7F is a cross-sectional view of the insertion guide tube splayedopen to accommodate a larger-dimensioned proximal region of thestimulating assembly, with arrows representing the twisting force of thestimulating assembly and the reactive forces applied to the stimulatingassembly by the insertion guide tube; and

FIG. 8 is a flowchart of a method in accordance with embodimentspresented herein.

DETAILED DESCRIPTION

Embodiments presented herein are generally directed to dual-functionsurgical tools for insertion of implantable stimulating assemblies, suchas intra-cochlear stimulating assemblies. In addition to facilitatingintra-operative positioning of a stimulating assembly within a recipient(e.g., operating to guide the stimulating assembly of an implantablemedical device into position), the surgical tool also includes aplurality of electrodes configured to apply an electroporationelectrical field to a recipient's nerve cells to enable introduction ofa treatment substance into the nerve cells.

As noted, there are a number of different types of tissue-stimulatingprostheses that use a stimulation assembly to deliver stimulation tocompensate for a deficiency in a recipient. Merely for ease ofillustration, details of insertion tools in accordance with embodimentspresented herein are primarily described herein with reference to theinsertion of a specific type of stimulating assembly (electrodeassembly), namely an intra-cochlear stimulating assembly of a cochlearimplant. However, it is to be appreciated that the insertion toolspresented herein may be used with other types of stimulating assembliesof other tissue-stimulating prostheses, such as spinal stimulators,vagal nerve stimulators, retinal stimulators, and deep brainstimulators.

More specifically, FIG. 1 is perspective view of an exemplary cochlearimplant system 100 with which embodiments presented herein may beutilized. The cochlear implant system 100 includes an external component102 and an internal/implantable component 104. The external component102 is directly or indirectly attached to the body of the recipient andtypically comprises an external coil 106 and, generally, a magnet (notshown in FIG. 1) fixed relative to the external coil 106. The externalcomponent 102 also comprises one or more sound input elements 108 (e.g.,microphones, telecoils, etc.) for detecting sound signals or input audiosignals, and a sound processing unit 112. The sound processing unit 112includes, for example, a power source (not shown in FIG. 1) and a soundprocessor (also not shown in FIG. 1). The sound processor is configuredto process electrical signals generated by a sound input element 108that is positioned, in the depicted embodiment, by auricle 110 of therecipient. The sound processor provides the processed signals toexternal coil 106 via, for example, a cable (not shown in FIG. 1).

The implantable component 104 comprises an implant body 114, a leadregion 116, and an elongate intra-cochlear stimulating assembly(electrode assembly) 118. The implant body 114 comprises a stimulatorunit 120, an internal/implantable coil 122, and an internalreceiver/transceiver unit 124, sometimes referred to herein astransceiver unit 124. The transceiver unit 124 is connected to theimplantable coil 122 and, generally, a magnet (not shown) fixed relativeto the internal coil 122.

The magnets in the external component 102 and implantable component 104facilitate the operational alignment of the external coil 106 with theimplantable coil 122. The operational alignment of the coils enables theimplantable coil 122 to transmit/receive power and data to/from theexternal coil 106. More specifically, in certain examples, external coil106 transmits electrical signals (e.g., power and stimulation data) toimplantable coil 122 via a radio frequency (RF) link. Implantable coil122 is typically a wire antenna coil comprised of multiple turns ofelectrically insulated single-strand or multi-strand platinum or goldwire. The electrical insulation of implantable coil 122 is provided by aflexible molding (e.g., silicone molding). In use, transceiver unit 124may be positioned in a recess of the temporal bone of the recipient.Various other types of energy transfer, such as infrared (IR),electromagnetic, capacitive and inductive transfer, may be used totransfer the power and/or data from an external device to a cochlearimplant and, as such, FIG. 1 illustrates only one example arrangement.

Elongate stimulating assembly 118 is configured to be at least partiallyimplanted in cochlea 130 and includes a plurality of longitudinallyspaced intra-cochlear electrical stimulating contacts (electricalcontacts) 128 that collectively form a contact array 126. Stimulatingassembly 118 extends through an opening in the cochlea 130 (e.g.,cochleostomy 132, the round window 134, etc.) and has a proximal endconnected to stimulator unit 120 via lead region 116 that extendsthrough mastoid bone 119. Lead region 116 couples the stimulatingassembly 118 to implant body 114 and, more particularly, stimulator unit120.

In general, the sound processor in sound processing unit 112 isconfigured to execute sound processing and coding to convert a detectedsound into a coded signal corresponding to electrical signals fordelivery to the recipient. The coded signal generated by the soundprocessor is then sent to the stimulator unit 120 via the RF linkbetween the external coil 106 and the internal coil 122. The stimulatorunit 120 includes one or more circuits that use the coded signals,received via the transceiver unit 124, so as to output stimulation(stimulation current) via one or more stimulation channels thatterminate in the stimulating contacts 128. As such, the stimulation isdelivered to the recipient via the stimulating contacts 128. In thisway, cochlear implant system 100 stimulates the recipient's auditorynerve cells, bypassing absent or defective hair cells that normallytransduce acoustic vibrations into neural activity.

Stimulating assembly 118 may be inserted into cochlea 130 with the useof an insertion tool in accordance with embodiments presented herein.FIG. 2 is a side view of an embodiment of an insertion tool 134 forimplanting stimulating assembly 118 into cochlea 130. In theillustrative embodiment of FIG. 2, the insertion tool 134 includes anelongate insertion guide tube 136 configured to be partially insertedinto cochlea 130. The elongate insertion guide tube 136 has a distal end138 from which the stimulating assembly 118 is deployed into the cochlea130. Insertion guide tube 136 also comprises a radially-extending stop140 that may be utilized to determine or otherwise control the depth towhich insertion guide tube 136 is inserted into cochlea 130. In otherwords, the insertion guide tube 136 includes a first section 145,referred to herein as an intra-cochlear section, that is configured tobe inserted into, and subsequently withdrawn from, the recipient'scochlea 130. The intra-cochlear section 145 extends from a proximal end143 located adjacent to the stop 140 to the distal end 138 of theinsertion guide tube 136.

In the example of FIG. 2, insertion guide tube 136 also includes anextra-cochlear section 147 that is mounted on a distal region of anelongate staging section 140 on which the stimulating assembly 118 ispositioned prior to implantation. A handle 144 is mounted to a proximalend of staging section 140 to facilitate implantation. The handle 144,staging section 140, and extra-cochlear section 147 collectively form anextra-cochlear portion of the insertion tool 134 that facilitatesintra-operative positioning and retraction of the insertion tool 134.

During use, stimulating assembly 118 is advanced from staging section140 into an insertion lumen (not shown in FIG. 2) of the insertion guidetube 136 via ramp 146. As described further below, after insertion guidetube 136 is inserted to the appropriate depth in cochlea 130,stimulating assembly 118 is advanced through the insertion lumen of theguide tube 136 so as to exit distal end 138.

In one embodiment, the stimulating assembly 118 is inserted into thecochlea via the round window 134 and, as such, the intra-cochlearsection 145 of insertion guide tube 136 is sized to fit through theopening covered by the round window membrane. For example, the outerdiameter (or diameter equivalent) of the intra-cochlear section 145 canbe about 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, or 1.6 mm. Thesize of the lumen within the insertion guide tube generally matches thestimulating assembly (although the insertion guide tube can accommodateoversized stimulating assemblies by, for example, splaying along a seamas the electrode is advanced). The stimulating assembly 118 can have adiameter of between about 0.3 mm and about 1.2 mm. Contemporarystimulating assemblies have a diameter that is approximately 0.8 mm atits thickest point, but the distal end (tip) of the stimulating assemblycan have a significantly smaller diameter, such as approximately 0.3-0.5mm.

In addition to enabling insertion of the stimulating assembly 118 intothe cochlea 130, the insertion tool 134 of FIG. 2 is also configured tointroduce substances into the recipient's cochlear nerve cells viaelectroporation. In other words, as described further below, theinsertion tool 134 is a dual-function device that is configured todeliver an electrical field to open pores in the cochlear nerve cells toenable the introduction of substances thereto, as well as to enableintra-operative placement of the stimulating assembly 118 into thecochlea 130. The substances that the insertion tool 134 introduce intothe cochlear nerve cells are generally and collectively referred toherein as “treatment substances” and may include, but are not limitedto, biological or bioactive substances, chemicals, pharmaceuticalagents, nanoparticles, ions, Deoxyribonucleic acid (DNA) molecules,Ribonucleic acid (RNA) molecules, proteins such as Brain-derivedneurotrophic factors, peptides, RNAi, viral vectors etc.

To enable the introduction of treatment substances via electroporation,the insertion tool 134 includes a plurality of electrodes 150. Alsoincluded in the insertion tool 134 is an electrical connection betweenthe electrodes 150 and a current source (e.g., external power source) sothat electroporation stimulation is provided to the electrodes. For easeof illustration, only a portion of the electrical connection between theelectrodes 150 and the current source, namely a plug 156 and anelectrical cable 158, are shown in FIG. 2. However, further details ofexample electrical connections are provided below.

Although FIG. 2 illustrates the use of a plug 156 in the electricalconnection between the electrodes 150 and the external power source, itis to be appreciated that other types of electrical connectors and otherelectrical connections may be used in other embodiments presentedherein. For example, in other embodiments the insertion tool 134 canincorporate a battery, the electrodes 150 can be electrically connectedto cochlear implant 100, etc.

The insertion tool 134 can also include a substance delivery mechanismformed, in the specific example of FIG. 2, by a substance delivery lumen(not shown in FIG. 2) and a syringe port 154. That is, a treatmentsubstance is delivered into the recipient's cochlea 130 via the syringeport 154 and a lumen extending through the intra-cochlear portion 147 ofthe insertion guide tune 136. In one example, at least the distal end138 of the insertion guide tube 136 is first inserted into the cochlea130 via an opening (e.g., the round window, oval window, cochleostomy,etc.) through which the stimulating assembly 118 is to be inserted intothe cochlea. With a syringe (not shown in FIG. 2) fluidically coupled tothe syringe port 154, a treatment substance is forced from the syringethrough the substance delivery lumen and out the distal end into thecochlea 130. As described further below, embodiments presented hereinmay make use of a number of other substance delivery mechanisms.

Once the treatment substance is delivered into the cochlea 130, theelectrodes 150 are configured to generate an electric field within thecochlea that increases the permeability of neural cell membranes. Inother words, current signals (electroporation stimulation) are deliveredto electrodes 150 in a manner that results in the generation of anelectrical field, sometimes referred to herein as an electroporationelectric field, that causes electroporation of the membranes of cochlearneural cells (i.e., creates pores or openings in the cell membranes). Asa result, the treatment substance can pass into the nerve cells throughelectrically opened pores in a cell membrane. As used herein,“electroporation” refers to the application of an electrical field to acell such that pores are opened in the cell membrane.

Before describing further details of insertion tools in accordance withembodiments presented herein, a brief explanation of electroporation andintroduction of a treatment substance into a cell is first providedbelow with reference to FIGS. 3A-3D. More specifically, FIGS. 3A and 3Care schematic diagrams illustrating a nerve cell prior to and during,respectively, electroporation in accordance with embodiments presentedherein. FIGS. 3B and 3D are enlarged views of a portion of the nervecell shown in FIGS. 3A and 3C, respectively.

FIG. 3A is a schematic diagram of a natural nerve cell 155 at rest priorto delivery of an electroporation electric field. As shown, the nervecell 155 comprises a cell membrane 156 that separates the interior 158of the nerve cell 155 from the surrounding area 160. Generally, the area160 is a fluid filled space.

FIG. 3B is an enlarged view of a portion 162 of nerve cell 155,including a portion of the cell interior 158, a portion of the cellmembrane 156, and the area 160 adjacent to the portion 162 of the cellmembrane. As shown in FIG. 3B, elements 164 of a treatment substance aredisposed in the area 160 adjacent the nerve cell 155.

As shown in the schematic diagram of FIG. 3C, once the treatmentsubstance (i.e., elements 164) is introduced into the proximity of thenerve cell 155, an electrical potential (i.e., voltage difference) 165is applied across the nerve cell 155 by electrodes of an insertion toolin a manner that causes electroporation of the nerve cell. Morespecifically, as shown in FIG. 3D, the electrodes of an insertion tool,such as electrodes 150 of insertion tool 134, generate an electricalfield that creates an electrical potential across the nerve cell 155that, in turn, opens up pores 166 in the cell membrane 156. Theelectrically opened pores 166 allow the elements 164 of the treatmentsubstance to enter the nerve cell 155 through the cell membrane 156(i.e., as the potential difference is applied to the cell, theelectrically opened pores in the cell membrane allow material to flowinto the cell). After the electrical potential 165 is removed, the pores166 in the cell membrane 156 close such that the elements 164 of thetreatment substance remain in the nerve cell 156.

FIG. 4A is a perspective view of the intra-cochlear section 145 ofinsertion guide tube 136 of FIG. 2. As shown in FIG. 4A, a plurality ofelectrodes (electrical stimulating contacts) 150 are located at theouter surface 171 of the intra-cochlear section 145, namely on the outersurface of an outer wall 188. The electrodes 150 may be disposed on oneor more selected portions of the outer surface 171 or maycircumferentially surround the longitudinal length of the outer surface171.

The electrodes 150 are electrically connected to a power supply (currentsource) via an electrical connector and one or more leads, such as wiresor traces, (not shown in FIG. 4A) extending through or along theintra-cochlear section 145. Some embodiments of the insertion tool 134include an electrical cable 158 and electrical connector (e.g., plug156) to connect the electrode leads to an external current source.Alternatively, the insertion tool 134 can incorporate a battery, such asa rechargeable Li-Ion battery pack or replaceable batteries that arehoused in a sealed compartment (allowing the tool to be adequatelysterilized). In both embodiments, the electrodes 150 are electricallyisolated from any power source of the cochlear implant 100.

As noted, the electrodes 150 are configured to generate an electricfield within the cochlea 130 that causes electroporation of the cochlearnerve cells. In one arrangement, the electrical field is generated viathe delivery of charge-balanced biphasic waveforms (i.e.,electroporation stimulation) to two groups of electrodes 150, whereinthe two groups alternatively source and sink the current. Morespecifically, a charge-balanced biphasic waveform comprises first andsecond current pulses having equal amplitude and duration, but anopposite polarity (i.e., one positive pulse and one negative pulse).Since the positive pulse equals the negative pulse, ideally, the netcharge transferred to the cochlea cells is zero. In certain embodiments,the current pulses have an amplitude in the range of 40-60 milliamps.

In one example, a first current pulse having a first polarity isdelivered in a first direction between two or more of the electrodes150, and then a second pulse having the reverse polarity is delivered ina second direction between the two or more electrodes 150. In operation,such a biphasic waveform is driven between the two or more electrodes150 a number of times (e.g., five times) in a selected pattern to affectthe electroporation.

In one specific arrangement, the electrodes 150 are separated into twofunctional groups based on their relative position within theintra-cochlear section 145, and these two electrode groups receive thebiphasic waveforms. More specifically, FIG. 4A illustrates that theelectrodes 150 located relatively closer to the distal end 128 of theinsertion guide tube 136 (e.g., the distal half of the electrodes) forma distal electrode group 170. The electrodes 150 within the distalelectrode group 170 are electrically connected to the power supply inmanner that allows all of the electrodes in the group to receivesubstantially the same current signals from the power supply. In otherwords, the electrodes 150 within the distal electrode group 170functionally operate as a single large electrode so as to collectivelydeliver biphasic current pulses (i.e., half of a biphasic waveform) tothe cochlea 130 with a first polarity.

FIG. 4A also illustrates that the electrodes 150 located relativelycloser to the proximal end 143 of the insertion guide tube 136 (e.g.,the proximal half of the electrodes) form a proximal electrode group172. The electrodes 150 within the proximal electrode group 172 areelectrically connected to the power supply in manner that allows all ofthe electrodes to receive substantially the same current signals fromthe power supply. In other words, the electrodes 150 within the proximalelectrode group 172 functionally operate as a single large electrode soas to collectively deliver a biphasic current pulse (i.e., half of abiphasic waveform) to the cochlea 130 with a second (opposite) polarity.

During delivery of a biphasic current pulse via the distal electrodegroup 170, the electrodes 150 in the proximal electrode group 172operate as returns for the delivered current. That is, the deliveredcurrent passes from the electrodes 150 of distal electrode group 170 tothe electrodes 150 of the proximal electrode group 172. Similarly,during delivery of a biphasic current pulse via the proximal electrodegroup 172, the electrodes 150 in the distal electrode group 170 operateas returns for the delivered current. That is, the delivered currentpasses from the electrodes 150 of proximal electrode group 172 to theelectrodes 150 of the distal electrode group 170.

In one example, the biphasic waveforms are provided in a square waveconfiguration where the pulses each have duration in the range ofapproximately 100 μs to approximately 500 ms. For example, the biphasicwaveforms can have a duration (pulse width) of approximately 5 ms, 10ms, 15 ms, 20 ms, 25 ms, 30 ms, 35 ms, 40 ms, 45 ms, or 50 ms. Multiplepulses are commonly used. The number of electroporation pulsesadministered is typically in the range of 5 to 200 pulses in total. Theinterval between each pulse can be about 1, 2, 3, 4, 5, 6, 7, 8, 9, or10 seconds. Ramped waveforms can be used in at least some embodiments,as ramped waveforms can provide a faster onset of electroporationdielectric breakdown of the cell membrane, while minimizing currentdelivery.

FIG. 4A illustrates a specific example in which the electrodes 150 areformed into two functionally separate electrode groups that deliver aform of bipolar stimulation. That is, in these arrangements, theelectroporation electrical field is generated via the delivery ofcharge-balanced biphasic current to two groups of electrodes 150,wherein the two groups alternatively source and sink the current.However, it is to be appreciated that the electrodes of an insertiontool in accordance with embodiments presented herein may be formed in anumber of different arrangements for delivery of pulses.

It is also to be appreciated that insertion tools in accordance withembodiments presented herein can make use of a number of differentelectrical stimulation strategies or modes including, for example, usingmonopolar stimulation, multipolar stimulation, common ground mode, etc.to cause electroporation of the cochlea nerve cells. In general, thevarious stimulation modes that may be used in the embodiments presentedherein differ from another in the shape of the electrical fieldgenerated within each stimulation mode. In these different modes, theelectrodes 150 may be organized into different functional groups an/orconfigurations. For example, in one embodiment, the electrodes 150 arearranged so as to generate a wide electrical field that causeselectroporation of a substantially large population of nerve cells. Thewide electrical field may be generated, for example, using a bipolarstimulation mode, a common ground stimulation mode, a monopolarstimulation mode, etc.

In certain embodiments, it may be desirable to limit the area of nervecells that are subject to electroporation. For example, it may be usefulto cause electroporation of nerve cells in a small part of the cochleahaving non-functional hair cells without affecting other parts of thecochlea. To this end, embodiments may make use of a stimulation modewhere a subset of the electrodes 150 operates in accordance with astimulation mode that generates a narrow or focused electrical field.The focused electrical field may be generated, for example, usingmultipolar stimulation (sometimes referred to as phased arraystimulation).

In accordance with certain embodiments, multipolar or other focusedstimulation modes may be used to “steer” the electric field to otherregions of the cochlea and/or the surrounding area so thatelectroporation can occur at other sites. Since some types of cells canbe damaged by repetitive stimulation, multipolar or other focusedstimulation modes could be used to steer the electroporation electricfield away from these types of cells.

As noted, FIG. 4A illustrates an embodiment in which the electrodes 150are located on the intra-cochlear region 145 of the insertion guide tube136. Depending on the insertion technique and location of the cochlearopening through which the insertion guide tube 136 is introduced intothe cochlea 130, the intra-cochlear region 145 may need to bend/flex. Assuch, the intra-cochlear region 145 of the insertion guide tube 136 isformed from an at least partially flexible material. The use of aplurality of relatively small electrodes, as shown in the arrangement ofFIG. 4A, rather than a few larger electrodes allows the intra-cochlearregion 145 to retain the ability to bend/flex.

In certain embodiments, the electrodes 150, as well as the leadsconnecting the electrodes to a power supply, may be formed as part of athin-film circuit that forms at least part of the outer wall 188. Morespecifically, in these embodiments, the outer wall 188 of the insertionguide tube 136 is configured as a substrate on which the electrodes 150and traces (i.e., the leads) are formed via thin-film deposition (i.e.,electrodes and traces are printed, etched or otherwise formed as a metallayer on the polymer substrate forming the outer wall of the insertionguide tube). Parts of the thin-film circuit can be coated with abiocompatible elastomer (such as medical grade silicone) to tune themechanical properties of the intra-cochlea section of insertion guidetube 188. Electrodes 150 are generally disposed on or recessed in theouter surface 171 of the outer wall 188.

The thin-film circuit can be formed into a sheath that comprises theintra-cochlea portion of the insertion tool. The outer dimensions of thesheath are generally defined by the size of the opening used to insertthe stimulating assembly into the cochlea (such as the round window) andthe prescribed insertion depth for the intra-cochlea section of the tool100. The size of the lumen or passage through the sheath is generallydefined by the stimulating assembly the insertion tool 100 is pairedwith. The sheath can have an outer diameter of between about 1 mm andabout 2 mm. The sheath can be configured to partially collapses orcompresses to fit an opening in the cochlea where the outer diameter ismarginally larger than the opening. The inner diameter of the sheath(the diameter of the lumen) is generally between about 0.4 mm and 1 mm.For example, the outer diameter can be about 1.2 mm, 1.3 mm, 1.4 mm or1.5 mm, and the diameter of the lumen can be about 0.5 mm, 0.6 mm, 0.7mm or 0.8 mm. The thin-film circuit can extend into the extra-cochleaportion of the tool to facilitate mechanical and electrical connectionbetween the respective (intra-cochlea and extra-cochlea) portions of thetool 100. The extra-cochlea portion of the tool can include sections ofthe thin-film circuit can also extend into an extra-cochlea section ofthe tool.

Thin-film deposition is an example of a technique that may be used toform the electrodes and leads of an insertion tool. In otherembodiments, the electrodes 150 may comprise metallic (e.g., platinum)contacts and the leads may comprise wires welded to the contacts. Inthese embodiments, the wires pass through the insertion guide tube 136for connection of the electrodes 150 to the power supply.

FIG. 4A illustrates an arrangement in which an insertion tool includes arelatively large number of small electrodes to deliver electroporationstimulation to a recipient. FIG. 4B is a perspective view of anintra-cochlear section 445 of another insertion guide tube in accordancewith embodiments presented herein that makes use of two relative largeelectrodes 450(A) and 450(B) to deliver electroporation stimulation.More specifically, electrodes 450(A) and 450(B) are located at the outersurface 471 of the intra-cochlear section 445, namely on the outersurface of an outer wall 488. The electrodes 450(A) and 450(B) can bedisposed on one or more selected portions of the outer surface 471 orcan circumferentially surround portions of the outer surface 471. In onexample, the electrodes 450(A) and 450(B) can half-band platinumelectrodes.

The electrodes 450(A) and 450(B) are electrically connected to a powersupply (current source) via one or more leads, such as wires or traces,(not shown in FIG. 4B) extending through or along the intra-cochlearsection 445. The electrodes 450(A) and 450(B) are configured to generatean electric field within a recipient's cochlea that causeselectroporation of the cochlear nerve cells. In one arrangement, theelectrical field is generated via the delivery of charge-balancedbiphasic waveforms to the electrodes 450(A) and 450(B), wherein the twoelectrodes alternatively source and sink the current. That is, firstcurrent pulse having a first polarity is delivered in a first directionbetween two electrodes 450(A) and 450(B, and then a second pulse havingthe reverse polarity is delivered in a second direction between the twoelectrodes 450(A) and 450(B). In operation, such a biphasic waveform isdriven between the two or more electrodes 450(A) and 450(B) a number oftimes (e.g., five times) in a selected pattern to cause electroporationof the cochlea cells.

In certain embodiments, the electrodes of an insertion tool arefunctionally organized in a pre-selected arrangement (e.g., presethardwired arrangement) that delivers electrical stimulation inaccordance with a pre-selected stimulation mode. However, in otherembodiments, the functional arrangement of the electrodes and/or theutilized stimulating mode is configurable (adjustable). For example,FIG. 5 is a schematic diagram illustrating an electroporation controlmodule 175 that may be disposed in the electrical connection 173 betweenelectrodes of an insertion tool, such as electrodes 150 of insertiontool 134, and a current source 176, such as an auxiliary (e.g.,external) power supply.

As shown, the electroporation control module 175 comprises a switchingcircuit 178 and a controller 180. The switching circuit 178 comprises aplurality of switches (not shown in FIG. 5) that are selectablyconnectable to either a positive signal line 182 of the current source176 (e.g., a wire connected to the positive pin of the external powersupply) or a negative signal line 184 of the current source 176 (e.g.,wire connected to the negative pin of the external power supply). Theswitches in the switching circuit 178 are also selectably connectable tothe electrodes that, in the arrangement of FIG. 5, are labeled aselectrodes 150(1)-150(N), via leads 185 (e.g., wires or traces). Ingeneral, the switching circuit 178 may have a number of differentconfigurations/arrangements that enable the electrodes 150(1)-150(N) tofunctionally operate as different groups that generate electroporationelectrical fields in accordance with various different stimulationmodes.

In addition, although FIG. 5 illustrates that the electrodes150(1)-150(N) are each connected to the switching circuit 178 viaseparate leads 185, it is to be appreciated that a plurality of theelectrodes may be electrically connected to the switching circuit 178via the same lead. In other words, subsets of the electrodes150(1)-150(N) may be hardwired as preset groups where each preset groupof electrodes is connected to the switching circuit 178 via a singlelead. In such embodiments, all the electrodes in the preset group ofelectrodes are activated together/simultaneously and functionallyoperate as a substantially larger contact.

As noted, the electroporation control module 175 also comprises acontroller 180. The controller 180 comprises, for example, amicroprocessor or digital logic gates in one or moreapplication-specific integrated circuits (ASICs), and operates tocontrol the arrangement of the switching circuit 178 and, in turn, thearrangement of the electrodes 150(1)-150(N) and the stimulation mode ofthe current signals. In certain embodiments, the controller 180 mayinclude, or be connected to, a user interface that allows a user toselect the arrangement for the electrodes 150(1)-150(N) and thestimulation mode of the current signals. In other embodiments, thecontroller 180 may be connectable to an external device (e.g., computer,remote control, etc.) via an interface. This can allow the user toselect the arrangement for the electrodes 150(1)-150(N) and thestimulation mode of the current signals via the external device.

In certain embodiments, an electroporation control module, such ascontrol module 175, may be fully integrated within an insertion toolpresented herein. In other embodiments, only a portion of theelectroporation control module 175 may be integrated within an insertiontool presented herein. For example, in one embodiment only the switchingcircuit 178 is integrated in the insertion tool and an interface forconnection to an external device is provided for control over theswitching circuit 178.

As noted above, prior to affecting electroporation of a recipient'snerve cells via an insertion tool, a treatment substance is firstdelivered into the cochlea so that the treatment substance is located inproximity to the nerve cells at the time the electroporation occurs.FIGS. 2 and 4 illustrate one example embodiment in which a substancedelivery mechanism is integrated within the insertion tool 134.

More specifically, the substance delivery mechanism of insertion tool134 is formed by a substance delivery lumen 152 and the syringe port154. In operation, a syringe is fluidically coupled to the syringe port154 and a treatment substance is forced from the syringe through thesubstance delivery lumen 152 and out from the distal end 128 into thecochlea 130. As shown in FIG. 4A, the substance delivery lumen 152 isintegrated within the outer wall 188 of the insertion guide tube 136defining a stimulating assembly insertion lumen 190.

It is to be appreciated that insertion tools in accordance withembodiments presented herein can comprise substance delivery mechanismsthat are different from that shown in FIGS. 2 and 4. For example, in onealternative arrangement, the syringe port 154 can be replaced by aconnection to another substance delivery device, such as a pump (e.g.,an infusion pump), reservoir, etc. In an alternative arrangement, thesubstance delivery lumen can be located within the stimulating assemblyinsertion lumen, rather than integrated within the outer wall of theinsertion guide tube.

FIGS. 6A and 6B illustrate a further arrangement that includes acollapsible substance delivery lumen located inside a stimulatingassembly insertion lumen, rather than a lumen integrated within an outerwall of an insertion tool. More specifically, FIGS. 6A and 6B arecross-sectional views of a distal portion 629(A) of an insertion tool.As shown, the distal portion 629(A) comprises an outer wall 688(A) thatdefines a stimulating assembly insertion lumen 690(A). Located withinthe stimulating assembly insertion lumen 690(A) adjacent to the outerwall 688(A) is a collapsible substance delivery lumen 652. Although notshown in FIGS. 6A and 6B, a proximal end of the collapsible substancedelivery lumen 652 is configured to be fluidically coupled to asubstance delivery device, such as syringe, reservoir, pump, etc.

In certain arrangements, the distal portion 629(A) of the insertion toolcannot exceed the size of an opening in a recipient's cochlear throughwhich the distal portion 629(A) is inserted. Due to these sizeconstraints, the size of the stimulating assembly insertion lumen 690(A)is limited and, accordingly, substantially all of the stimulatingassembly insertion lumen 690(A) may be needed to accommodate thestimulating assembly (i.e., the stimulating assembly may substantiallyfill the stimulating assembly insertion lumen 690(A)). These sizeconstraints may limit the size of a substance delivery lumen, as well aswhere a substance delivery lumen may be located.

The collapsible substance delivery lumen 652 of FIGS. 6A and 6B providesa substantially large lumen for delivery of a treatment substance to arecipient while minimizing and/or eliminating a requirement for a largerdistal portion 629(A) of an insertion tool. In particular, as shown inFIG. 6A, the collapsible substance delivery lumen 652 has a firstexpanded (non-compressed) configuration that enables a treatmentsubstance to pass there through and exit out from a distal end 628(A) ofthe insertion tool. Although the expanded configuration of FIG. 6Aallows for passage of the treatment substance, this expandedconfiguration also occupies a region of the stimulating assemblyinsertion lumen 690(A) that may be needed for insertion of thestimulating assembly. However, the collapsible substance delivery lumen652 has a compressible arrangement such that, when a stimulatingassembly is inserted into the stimulating assembly insertion lumen690(A), the stimulating assembly will substantially collapse thedelivery lumen 652 against the outer wall 688(A) (i.e., the collapsiblesubstance delivery lumen 652 is compressed in response to pressureapplied by a stimulating assembly introduced into the stimulatingassembly insertion lumen 690(A)).

FIG. 6B illustrates the collapsible substance delivery lumen 652 in acollapsed (compressed) configuration. However, for ease of illustration,the stimulating assembly introduced into the stimulating assemblyinsertion lumen 690(A) to cause the compression of the collapsiblesubstance delivery lumen 652 has been omitted from FIG. 6B.

FIG. 6C is cross-sectional view of another embodiment in which aninsertion tool includes an alternative treatment substance deliverymechanism. More specifically, shown in FIG. 6C is an insertion guidetube 636 of an insertion tool. The insertion guide tube 636 includes anintra-cochlear section 645 and extra-cochlear section 647. The insertionguide tube 636 includes an outer wall 688(C) that defines a stimulatingassembly insertion lumen 690(C).

An opening/inlet 691 is formed in the outer wall 688(C) atextra-cochlear section 647. Although not shown in FIG. 6C, this opening691 is configured to be fluidically coupled to a substance deliverydevice, such as syringe, reservoir, pump, etc. so that a treatmentsubstance may be delivered into the stimulating assembly insertion lumen690(C). The delivery of a treatment substance to lumen 690(C) isgenerally represented in FIG. 6C by arrow 693.

As shown in FIG. 6C, when a treatment substance is delivered into thelumen 690(C), the stimulating assembly 118 is retracted so that thetreatment substance is injected into an unobstructed section of thelumen with the distal end of the stimulating assembly positionedproximal to the injection site. In these embodiments, the stimulatingassembly 118 can help propagate and mix the treatment substance withinthe cochlea as it is advanced through the stimulating assembly insertionlumen 690(C).

As noted, the above embodiments are illustrative of drug deliverymechanisms that may be incorporated within an insertion tool inaccordance with embodiments presented herein. It is also to beappreciated that an insertion tool may be used with a treatmentsubstance that is first delivered to a recipient's cochlea via aseparate delivery device, such as a syringe, pump, etc. In suchembodiments, the insertion tool is inserted into the cochlea after thetreatment substance has already been delivered to the cochlea.

FIGS. 7A-7F are different views of embodiments of an insertion guidetube, referred to herein at insertion guide tube 736, forming part of aninsertion tool in accordance with embodiments presented herein. Theinsertion guide 736 is representative of an embodiment for use with apre-curved stimulating assembly. However, it is to be appreciated thatthese embodiments are merely illustrative and that the embodimentspresented herein may be used with other devices configured for insertionof, for example, straight stimulating assemblies. For ease ofdescription, features of the guide tube 736 will be described withreference to the orientation of the guide tube illustrated in the FIGS.7A-7F.

FIG. 7A is a partial cross-sectional view of an embodiment of insertionguide tube 736. As may be seen, insertion guide tube 736 includes ananti-twist section 721 formed at the distal end of the guide tube.Anti-twist section 721 is contiguous with the remaining part of guidetube 736. Guide tube 736 has an insertion lumen 790 which, in proximalsection 725 has a vertical dimension 727 and in distal anti-twistsection 721 has a smaller vertical dimension 717 described below. Thevertical dimension of insertion lumen 790 decreases from dimension 727to dimension 717 due to a ramp 749 at the proximal end of anti-twistsection 721.

Anti-twist section 721 causes a twisted stimulating assembly travelingthrough guide tube 736 to return to its un-twisted state, and retainsthe stimulating assembly in a straight configuration such that theorientation of the stimulating assembly relative to the insertion guidetube 736 does not change.

As shown in FIG. 7C, stimulating assembly 118 has a rectangularcross-sectional shape, with the surface formed in part by the surface ofthe electrode contact, referred to herein as top surface 751, and theopposing surface, referred to herein as bottom surface 753, aresubstantially planar. These substantially planar surfaces are utilizedin embodiments of the insertion guide tube described herein.

Tube wall 788 in anti-twist section 721 has surfaces 733 and 757 whichextend radially inward to form an anti-twist guide channel 781.Specifically, a superior flat 733 provides a substantially planar lumensurface along the length of section 721. As shown best in FIGS. 7A, 7Band 7D, superior flat 733 has a surface that is substantially planar andwhich therefore conforms with the substantially planar top surface 751of stimulating assembly 118. Similarly, inferior flat 757 has a surfacethat is substantially planar which conforms with the substantiallyplanar bottom surface 753 of stimulating assembly 118. As shown in FIG.7D, when a distal region of stimulating assembly 118 is located inanti-twist section 721, the surfaces of superior flat 733 and inferiorflat 757 are in physical contact with top surface 751 and bottom surface753, respectively, of the stimulating assembly.

Due to the longitudinal length of anti-twist guide channel 781,stimulating assembly 118 is unable to twist to relieve the stress causedby the inability of the stimulating assembly to assume its pre-curvedconfiguration. This is illustrated in FIG. 7A. As shown by arrow 706 inFIGS. 7E and 7F, stimulating assembly 118 is attempting to twist whilelocated in anti-twist section 721. As top surface 751 of stimulatingassembly 118 pushes against superior flat 733, the flat applies areactive force 704 to the assembly. Similarly, as bottom surface 753 ofstimulating assembly 118 applies a force against inferior flat 757, thatflat applies a reactive force 702 to the assembly.

Stimulating assemblies may be longitudinally tapered. To accommodate theincreasingly larger cross-sectional dimensions of a stimulating assembly118 as it passes through anti-twist guide channel 781, insertion guidetube 736 has a longitudinal seam 761 as shown in FIGS. 7A, 7B, 7D, and7E. This seam 761 enables insertion tube 736 to splay open as shown inFIG. 7F. Specifically, insertion tube 736 opens as the vertical distance791 from bottom surface 753 to top surface 751 of the portion of theassembly in guide channel 781 becomes greater than the vertical distance717 between the surfaces of inferior flat 757 and superior flat 733.

Once stimulating assembly 118 is inserted into cochlea 130, insertionguide tube 736 is retracted over stimulating assembly 118. The expandedinsertion guide tube 736 is to be withdrawn from cochlea 130 andtherefore is to pass through the cochleostomy, oval or round window. Ina round window insertion, for example, splayed insertion guide tube 736is to pass through round window aperture 708.

As stimulating assembly 118 is advanced through insertion guide tube736, the tendency of the assembly to twist decreases. This is due to theincreasingly greater portion of the stimulating assembly which has beendeployed, the relatively larger dimensions of the proximal regions ofthe assembly, and the relatively smaller bias force in the proximalregion as compared to the distal region of the assembly. Thus, as thecross-sectional size of the assembly passing through guide channel 781increases, the tendency of the stimulating assembly to twist decreases.Referring again to FIG. 7F, as insertion guide tube 736 splays, thehalves of bifurcated superior flat 733 each translate laterally to thecorners of the stimulating assembly, and ultimately to opposing sides ofthe assembly. Thus, the extent to which superior flat 733 prevents thetwisting of the stimulating assembly decreases with the tendency of theassembly to twist. And as noted, the outside diameter of insertion guidetube 736 does not exceed threshold value(s) which facilitate thewithdrawal of the guide tube. In the example noted above with referenceto FIGS. 7E and 7F, for example, insertion guide tube 736 has a diameterthat is less than the round window aperture 708 when the guide tube isand is not splayed.

As shown in FIG. 7D, lumen 790 has a lateral dimension or width 795which is greater than the analogous lateral dimension or width 793 ofthe distal region of stimulating assembly 118. This space is dimensionedto receive the wider stimulating assembly as the larger proximal regionpasses through guide channel 781.

In anti-twist section 721 there is a minimal gap, if any, between flats733, 757 and stimulating assembly 118, thereby enabling anti-twist guidechannel 781 to closely control the orientation of the assembly, as notedabove. Should a region of stimulating assembly 118 located in proximalsection 725 be partially twisted relative to a region that is inanti-twist guide channel 781, ramps 749 facilitate the rotation of theassembly as it enters the guide channel. This eliminates the relativetwist of this region relative to a more distal region of the assembly.This places top and bottom surfaces 751, 753 in parallel with thecorresponding surfaces of superior flat 733 and inferior flat 757thereby enabling the assembly to continue through anti-twist guidechannel 781. In other words, for the assembly to travel through guidechannel 781, the assembly has to be substantially straight. As theassembly travels up ramp 749, the ramp facilitates the rotation of theassembly to enable the assembly to enter guide channel 781.

In an exemplary embodiment, insertion guide tube 736 is made ofpolyimide, and the flats comprise silicone molded in the tube. Othermaterials can be utilized in other embodiments. In some embodiments, theflats and guide tube are unitary.

FIGS. 7A-7F have been described above with reference to the operation ofthe insertion guide tube 736 during insertion of stimulating assembly118 into a recipient's cochlea 130. As noted above, the insertion guidetube 736 is a component of a dual-function insertion tool. That is, inaddition to enabling correct insertion of the stimulating assembly 118into the cochlea 130, the insertion tool is further configured todeliver an electrical field to open pores in the cochlear nerve cellsand thereby enable introduction of substances thereto. As such, theinsertion guide tube 736 further comprises a plurality of electrodes 750disposed on an outer surface of the tube wall 788. Similar to the aboveembodiments, the electrodes 750 are configured to generate an electricalfield in the cochlea so as to affect electroporation of cochlear nervecells. The plurality of electrodes 750 are electrically connected to apower supply by an electrical connection (not shown in FIGS. 7A-7F)extending through the insertion guide tube 736.

In addition to the plurality of electrodes 750, the insertion guide tube736 also includes a substance delivery lumen 752 that delivers atreatment substance to the cochlea 130. In the example of FIGS. 7A-7F,within the proximal section 725 of the insertion guide 736, thesubstance delivery lumen 752 is integrated within the tube wall 788. Thesubstance delivery lumen 752 is configured to follow the ramp 748 and isintegrated within the superior flat 733 within the anti-twist section721.

FIG. 8 is a method 800 for introducing a treatment substance into nervecells of a cochlea with a surgical tool in accordance with embodimentspresented herein. Method 800 begins at 802 where the surgical tool ispositioned in the cochlea of a recipient (e.g., an intra-cochlearportion of the surgical tool is inserted into the cochlea). At 804, anelectrical field is generated between at least two electrodes disposedon an intra-cochlea portion of the surgical tool. At 806, an electrodeis advanced into the cochlea via the surgical tool. At 808, the surgicaltool is withdrawn from the cochlea.

It is to be appreciated that the order of the operations shown in FIG. 8is merely illustrative.

It is to be appreciated that the embodiments presented herein are notmutually exclusive.

The invention described and claimed herein is not to be limited in scopeby the specific preferred embodiments herein disclosed, since theseembodiments are intended as illustrations, and not limitations, ofseveral aspects of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

What is claimed is:
 1. A surgical tool comprising: an intra-cochlearportion configured to be inserted into the cochlea of a recipient toguide a stimulating assembly of an implantable medical device intoposition within the cochlea, wherein the intra-cochlear portion of thesurgical tool comprises a plurality of electrodes.
 2. The surgical toolof claim 1, wherein the intra-cochlear portion comprises a sheath, andwherein the electrodes form part of the sheath.
 3. The surgical tool ofclaim 2, wherein the sheath comprises a thin-film circuit, and whereinthe electrodes are formed on an outer surface of the thin-film circuit.4. The surgical tool of claim 1, wherein the surgical tool has anextra-cochlear portion that facilitates manipulation of the surgicaltool during surgery.
 5. The surgical tool of claim 1, wherein theintra-cochlear portion is configured for insertion through the roundwindow of the cochlea.
 6. The surgical tool of claim 4, furthercomprising an insertion guide tube that extends from the extra-cochlearportion to the intra-cochlear portion of the surgical tool, wherein thesurgical tool is configured to advance the stimulating assembly throughthe insertion guide tube into the cochlea.
 7. The surgical tool of claim6, wherein the surgical tool includes a slide mechanism that advancesthe stimulating assembly through the insertion guide tube.
 8. Thesurgical tool of claim 1, wherein the surgical tool has at least oneelectrical connector configured to electrically connect the electrodesto a current source.
 9. The surgical tool of claim 8, wherein theelectrical connector is configured to electrically connect the surgicaltool to an external current source.
 10. The electrode insertion tool ofclaim 1, wherein the electrodes are electrically isolated from theimplantable medical device.
 11. An insertion tool for an intra-cochlearstimulating assembly, comprising: an insertion guide tube having aninsertion lumen configured to receive the intra-cochlear stimulatingassembly therein, wherein a distal portion of the insertion guide tubeis configured to be positioned within a cochlea of a recipient; and oneor more electrodes disposed on the distal portion of the insertion guidetube, wherein the one or more electrodes are configured to apply anelectrical field to the cochlea.
 12. The insertion tool of claim 11,further comprising: a least one electrical connector configured toelectrically connect the electrodes to a current source; and one or moreleads extending from the one or more electrodes to the electricalconnector.
 13. The insertion tool of claim 11, wherein the one or moreelectrodes comprise a plurality of electrodes formed into two or morefunctional groups of electrodes.
 14. The insertion tool of claim 13,wherein the two or more functional groups of electrodes include a distalgroup of electrodes comprising electrodes located relatively closer to adistal end of the insertion guide tube, and a proximal group ofelectrodes comprising electrodes located relatively closer to a proximalend of the insertion guide tube.
 15. The insertion tool of claim 11,wherein an outer surface of the insertion guide tube comprises athin-film circuit, and wherein the one or more electrodes are formed aspart of the thin-film circuit.
 16. The insertion tool of claim 11,further comprising: a substance delivery lumen configured to deliver atreatment substance into the cochlea.
 17. The insertion tool of claim16, wherein the substance delivery lumen is a collapsible lumen that islocated inside the insertion lumen of the insertion guide tube.
 18. Theinsertion tool of claim 11, wherein the treatment substance is at leastone biological agent selected from the group including: Deoxyribonucleicacid (DNA), Ribonucleic acid (RNA) molecules, brain-derived neurotrophicfactors, peptides, RNAi and viral vectors.
 19. The insertion tool ofclaim 11, wherein the insertion guide tube includes a longitudinal seamthat is configured to splay open as a force is applied to an interiorsurface of the insertion guide tube.
 20. A method comprising:positioning a surgical tool in the cochlea of a recipient; generating anelectrical field between at least two electrodes disposed on anintra-cochlea portion of the surgical tool; advancing, via the surgicaltool, an electrode into the cochlea; and withdrawing the surgical toolfrom the cochlea.
 21. The method of claim 20, further comprisingdelivering a treatment substance into the cochlea.
 22. The method ofclaim 20, comprising sequentially: delivering a treatment substance intothe cochlea, positioning the surgical tool in the cochlea, andgenerating an electrical field between at least two electrodes disposedon an intra-cochlea portion of the surgical tool.
 23. The method ofclaim 20, wherein generating the electrical field comprises: generatingthe electrical field via the delivery of charge-balanced biphasiccurrent to two groups of electrodes, wherein the two groups ofelectrodes alternatively source and sink the current.
 24. The method ofclaim 21, comprising generating an electrical field with a magnitude anda duration selected to increase the permeability of cell membranes toenhance introduction of the treatment substance into the cells.
 25. Themethod of claim 20, comprising advancing the electrode, through a lumenin the surgical tool, from an extra-cochlea position to an intra-cochleaposition.